Hydrocarbons can be transferred from an undersea pipeline, such as one which leads to undersea wells, to tankers at the sea surface, by a variety of types of offshore terminals. Under severe environmental conditions, such as where there are intrusions of ice packs as well as severe storms, it is desirable to enable a tanker to disconnect from the terminal to sail away, while much of the terminal sinks a considerable depth below the sea surface to lie free of much of the severe environmental conditions. One type of offshore terminal which can be used under these conditions includes a riser having a lower end that is loosely anchored to the sea floor, as through a group of catenary chains. The chains hold the riser deep under water but above the sea floor, while enabling the riser to be easily lifted up to the vessel. Improvements in such a system which facilitated connection of the top of the riser to the vessel and which provided improved mooring at minimal cost, would be of considerable value.